Fix print displacement on SAC, CNS and OTUs

Changes in print_weight had displaced the plot of next prints.
This fix the displacement using cairo_save/restore.

Signed-off-by: Salvador Cuñat <salvador.cunat@gmail.com>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
Fixing SP handling in planner, adding event

Fixes bug in planner which prevents from bailing out (setpoint = 0).

Also introduces events for changing setpoints in planner.
It also makes the eventtype for gaschange slightly more consistent by
changing it from SAMPLE_EVENT_GASCHANGE (O2 only) to
SAMPLE_EVENT_GASCHANGE2 (O2/He). But Subsurface treats them both the same
(the distinction comes from libdivecomputer).

Signed-off-by: Jan Schubert <Jan.Schubert@GMX.li>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
Fixing SP handling in planner, adding event

Fixing the SP change event and introducing a bailout scenario.

I decided not to use a event showing SP=0.0 nor using a gaschange event as
is in fact there is no gas change related to bailing out itself. If there
is also a gaschange for the event it will be displayed anyway.

Signed-off-by: Jan Schubert <Jan.Schubert@GMX.li>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
Fixing SP handling in planner, adding event

This moves some double/floating handling for po2 to plain integer. There
are still non int values around (also for phe and po2) in the plot area.

Signed-off-by: Jan Schubert <Jan.Schubert@GMX.li>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>